This program is designed to investigate the host-range, cellular relationships and growth dynamics in arthropods or their cells of vector-borne pathogenic microorganisms, particularly arboviruses. Efforts are made to develop systems of arthropod (acarine and insect) tissue and cell culture and to apply them to the study of vector-borne disease agents. Arboviruses and rickettsias are tested for ability to propagate in these cultures and the ranges of pathogen supporting ability of the cell systems are thus defined. After prolonged growth in vitro and at the relatively low temperatures required by insect cells, pathogens are tested for changes in strain, virulence or antigenic characteristics. By contract with a collaborating laboratory overseas, critical factors influencing the survival of tick vectors of disease agents and of these agents within the vectors themselves are being investigated from a biochemical and physiological standpoint. This last portion of the project also provides basic descriptive information necessary for progress in developmental tick tissue culture studies.